Many people have said that the best way to see the bits of America between New York and the West Coast is from 35,000 feet with a cocktail in your hand.

Those people never saw it like we did it for a month last summer - on hired Harley-Davidsons, the all-American motorbikes, coast to coast. We rode from New York to San Francisco, a total of 3,122 miles by the most direct route but nearer 5,000 miles after a few detours. (If we had gone the other way from London, we would have reached India.)

It was a journey to make most motorbiking aficionados green with envy. America? On a Harley? You bastard. It was wide open country, the freedom of the road that you get in very few other places, where you know the showers are going to work wherever you end up at the end of the day. And a month away, no responsibilities, no work, no kids. The other in this equation was my Hampstead doctor friend, John.

The best bits? We both agreed that racing a mile-long freight train along a deserted part of Route 66 in Arizona, reaching the front and having the driver blow his mournful whistle was fantastic. We were not sure whether we were laughing or crying with pleasure.

Then there was the drive towards Monument Valley, the scene of all those Westerns with the sandstone buttes and mesas looming either side of the road. And there was the night in Mexican Hat, a dusty town of 34 people just north of the Valley, where we spent the night with a group of Harley riders down from Detroit for a wedding and the motel owner, his daughter and his son played exquisite country music until the early hours, under a clear star-studded sky while we ate steak and drank cold beer.

The worst bits? Not many but day one was hot, the roads into and out of New York were heaving and we were on big bikes that we were not used to - 1,450cc of Harley Road Kings. One each. Driving through New York, past the Empire State Building, should have been fun but with the temperature up in the 90s, it wasn't. And neither was the New Jersey Turnpike. It sounds much better in the songs.

The plan was simple - drive Route 50, a two-lane blacktop most of the way from coast to coast, basically through the middle of America, staying at $40 a night motels. Which is what we did.

On the roads in the east, through the tree-clad mountains of Virginia, there were roadside exhortations galore - one saying that BIBLE spelt Basic Information Before Leaving Earth; another saying that there was a coffee morning with Christ at 11am. We were 20 minutes late for that world exclusive. Then there were the heartbreakingly evocative small towns of the mid-west, where one pleaded on a billboard: Don't Overlook Burlingame. But I am afraid we did.

And many places had that feeling, with abandoned farmhouses and homesteads, that people were just leaving town, never to return, heading for the coast. As one guy said when we asked who stayed here: "People who ain't got to where they were going to."

In Madison, on the banks of the Ohio, we met a young woman who had never seen the ocean but hoped to go to Florida soon. But while many of these places felt like a scene from the Last Picture Show, there were, for the tourist, wonderful moments. The undulating farmland of Illinois, thundering across the flatlands of Kansas, racing a hail-storm and winning, following bits of the Santa Fe trail and heading west.

There was that feeling, that we never get in Europe, of just travelling - that if the road went on forever, then so could we. It took us two days to cross Kansas which is very, very, very flat. But we were at what seemed like 45 degrees because the cross wind was so strong. And it was hot, too, so much so that when a truck passed by it felt you were in a tumble dryer.

We did reach middle America, but when we got there, the only people we saw were from Louisiana. In the town of Kinsley, Kansas, on US50, there is a sign that points to New York 1,561 miles east, and to San Francisco 1,561 miles west. Halfway across. With a few of our detours, we had done 1,878 miles.

The Rockies loomed ahead. And on the western side we found motorbike heaven. We rode down the canyon of the Colorado on Highway 128 for 25 miles, mesmerised by the sweep of the river and the towering cliffs on both sides, and then visited the Arches National Park, where there are numerous sandstone arches and towering spires sprouting out of the desert.

We met some Harley bikers along the way and drank beer and ate steaks with them in Moab, an old uranium mining town. We stayed at the Apache Hotel, which numbered John Wayne among its former guests. With every second motel claiming that Wayne had had a fight in their establishment, it was a surprise that he had time to make any movies. It was perfect Western country, dramatic scenery and thousands and thousands of acres of wilderness - red-earthed desert, sage brush and tumbleweed.

Earlier in the day, we had ridden into the Canyonlands National Park, another spectacular deserted place with canyons and huge flat-topped mesas. You can feel a long way from anywhere out here, but some people choose to live in these beautiful but inhospitable places, while some less fortunate, the native Americans, have no choice.

Two of the former run a small trading post just outside the Canyonlands park entrance. Tracey and her husband moved from California six years ago and own a square mile of desert and rock. They run their shop and cafe and gas station, and live in a caravan. They have to collect their own water in a tank on the back of their truck, their power comes from solar panels, and their line of communication is a cellphone with a huge aerial. Business is precarious but Tracey said that her life had balance.

Utah is one of those few Western states where you do not have to wear a helmet, and, sorry mother, but I had my fingers crossed when I promised I would keep it on. It was wonderful, wind in your hair, blah blah blah. In a moment of excitement, I even bought a Stars and Stripes bandana (which blew off somewhere along the way).

So how was it, spending all day and night with one person for a month? Surprisingly, we did not fall out although we agreed that he snored more than me (we had to wear our earplugs in bed as well as on the bikes), and that my feet smelled the worst after a long day's ride (we rode an average of 200 miles a day, the most being 450 across Kansas).

The amount of faffing we both did drove the other mad at times. Motor bike riders, especially when you are on the road with two panniers with everything inside them, do a lot of faffing. Where did you last see those gloves? Which side did you pack the map/guidebook/water bottle? Did you remember to put the top back on your talcum powder because otherwise it will go everywhere and ruin that pannier (which it did)? Did I put my wallet in my inside pocket? Is that jacket strapped on the back going to fall off, because it looks to me as if it is going to (it did)? Where did you put the name of that motel we should be looking for? You underlined it somewhere, but where is that? Unpacking and packing every night. We never really improved at it. It was faff central.

Of course we ended up buying stuff along the way and having to squash everything ever tighter. I had a pair of training shoes that got so annoying to pack and so unused that I dumped them in a gas station garbage can. You can't really go on a shopping spree when on holiday with a Harley.

We had a couple of breakdowns - mechanical rather than emotional - and both on my bike. The gear shift, which you operate with your foot, came loose as we were coming into Kansas City, some of which, confusingly is in Missouri. We had just passed a pedestrian walking the other way carrying a 12ft cross draped in the Stars and Stripes. You could tell we were in America - it had a wheel on the long end.

Anyway, John strapped the shift up with a piece of rope. Later that day, the carburettor played up but by one of those happenstances we met a Harley nut that day and he put the bike on the back of his truck and drove us to a dealer where they sorted it out. Heaven knows what would have happened if we had been out in the desert or in the middle of nowhere. Circling vultures, cue chilling music.

We had a couple of days R&R in Vegas, where the doorman of the Four Seasons didn't bat an eyelid when we roared up to the front door of the smartest hotel in town (the only one without a casino) in sweaty T-shirts and jeans. We had a whole day off the bikes, which was weird. Then we drove off in the early morning to avoid the heat, through the desert to the cool mountains ringing LA and over into the city.

A couple of days up the coast on the highway one, a great ride with great fog, and we were in San Francisco. And there we said a reluctant goodbye to our bikes and the great American road.

PS: I take back what I said at the beginning. There's a lot to be said for a cocktail at 35,000 feet. It was the perfect way to toast an awfully big adventure.

11 tips for touring America on a Harley

1. Take a digital camera - that way, you can take pictures as you go and then delete the 90% that are rubbish every evening.

2. Take Road Trip USA (Moon Travel Handbooks, £17.99), which has descriptions of lots of different routes across the US, all off the interstates, and is well written in a laid-back way. We also had a state-by-page road map of the US. Big, unfolding ones are just too much trouble and blow about.

3. Take factor-30 sun cream and long-sleeved shirts or T-shirts to ride in the sunshine.

4. Go to the movies in small-town America - some of the cinemas are wonderful. Try the art deco Egyptian Theatre in Delta, Colorado.

5. We avoided the chain motels wherever possible. That way, we met Bob Wombacher at his motel, Bashful Bob's in Page, Arizona. Read his poetry at lightverse.net.

6. Don't go through America expecting good food, although the sirloin at Plaza III in Kansas City was possibly the best I have ever tasted. Stick to big breakfasts and steaks. Most people don't drink wine.

7. Try to keep the miles a day to a minimum. You'll never pass this way again so if you miss something, you really have missed it.

8. You can't miss the Grand Canyon. It is pretty grand. Book accommodation ahead only when going to big tourist areas like the Canyon (we stayed at the North Rim, far less busy than the South Rim.)

9. Put a Union flag on the bike, it will get people talking. Among them was a former Vietnam special forces man, with wife, on a Harley Fat Boy (the bike's name), who insisted on telling us how he had killed a guy in a motel fight.

10. Take three pairs of socks and underpants, one pair of jeans for wearing on the bike and another for the evening. Don't take too many shirts. One pair of bike boots and one pair of light shoes. Cut down on bath stuff - motels have towels, so don't take one; and don't shave. Rugged or what?

11. Thank the wife when you get home.

Way to go

Getting there: We flew from London Heathrow to New York and back from San Francisco on Virgin Atlantic (01293 747747, virgin.com/atlantic). In economy, that costs from £195 until March 31. In Upper Class, where you get lotsa cocktails at a bar, food when you want, legroom and massages, it costs from £1,864.

Bike hire: We rented our Road Kings through the Harley-Davidson Authorised Rentals programme which can be seen at hdrentals.com. Rentals can be made in many parts of the US and the world. The bikes came from Lighthouse Harley-Davidson on Long Island and cost $999 a week each. Rental rates vary with each operator. The bikes are all low-mileage, up-to-date models.

Where to stay: Our motels cost around $40 per room per night apart from the Four Seasons (00800 64886488 fourseasons.com) in Las Vegas ($225) and in San Francisco ($469).

Further information:Country code: 001. Flight time Heathrow-New York: 8 hrs. Time difference: New York City -5hrs, San Francisco -8hrs. £1 = $1.61.